Porous ceramic films may be formed in a variety of ways to produce semiconductor-quality substrate coatings. In the surfactant-templated method, for example, formation of porous ceramic films, a silica precursor solution used for evaporative-coating of a thin mesoporous silica film on to a silicon wafer is typically composed of a silica/silicate precursor, e.g. TEOS (tetraethyl orthosilicate), a surfactant and water dissolved in a polar organic solvent such as an alcohol, glycerol, or other suitable polar solvent. (See U.S. Pat. No. 5,922,299). The solution is aged for a set time and at a set temperature to allow for the formation of a specific range of sizes of oligomeric hydroxylated silica units. The hydrolysis reaction is catalyzed by the addition of a small amount of acid or base, and to generate the ultimate porosity, a surfactant (non-ionic or ionic) is used as a pore former in the deposition solution mixture. After evaporation-coating onto a silicon wafer, the wafer essentially has a “green” film (oligomeric highly hydroxylated silica units mostly in solid phase with trace amounts of the volatile components).
The green film is dried to remove any remaining solvent and catalyst and to facilitate some consolidation of the structure. Then the film is calcined (heated) to complete or carry out further cross-linking between oligomeric silica units. The drying steps typically are carried out at lower temperatures (approximately 100-200° C.) while the calcinations is carried out at more elevated temperatures (approximately 250-450° C.). Following calcinations, the porous ceramic film is chemically treated to dehydroxylate and hydrophobize the film producing a low dielectric film with high mechanical integrity. There can be variations to this approach of making nanoporous silicate films, including but not limited to variations in the solvent system, silica precursor, or type of pore former, but the procedure described above can be considered as a good example.